July 26, 2012 -- Working the night shift or any non-traditional schedule may increase your risk of heart attack and stroke, a study shows.

Previous research has linked shift work to heart disease and stroke risk factors including high blood pressure, high cholesterol levels, and diabetes. Now, researchers who reviewed 34 studies of more than 2 million people found that shift workers are also more likely to have a heart attack or stroke.

The new study "provides a firm anchor to state that shift work is associated with an increased risk of heart attack and stroke. The relationship is probably causal, but it is difficult to say that on the basis of observational studies alone," says study researcher Daniel G. Hackam, MD, PhD. He is an assistant professor of medicine at the University of Western Ontario, Canada.

The study is published online in the journal BMJ.

Exactly how shift work increases the risk for heart attack and stroke is not fully understood. It may disrupt the body's natural sleep-wake cycle. Shift workers may also be more likely to smoke and eat an unhealthy diet. And they may be less likely to get regular physical activity.

In the study, shift work was defined as:

night shifts

rotating shifts

split shifts

any non-daytime schedule

Night shift workers in the study had the highest risk for heart attack and stroke, particularly in the first 10 to 15 years on the job.

Shift Work Linked to Heart Attack, Stroke

Compared to people who worked during the day, shift workers were:

23% more likely to have a heart attack

5% more likely to have a stroke

But the study also showed that shift workers were not more likely to die compared to daytime workers.

The findings held up even when the researchers took into account unhealthy behaviors and other factors that increase heart attack and stroke risk.

Prevention is key, Hackam says. "If you are a shift worker, know your cardiovascular risk factors cold. Go see your family doctor and get an annual physical. And ask for measurement of your blood pressure, waist circumference, cholesterol, triglycerides, and fasting blood sugar."

Glenn Jacobowitz, MD, agrees that shift workers are a high-risk group. He is an associate professor of surgery and vice chief of vascular surgery at New York University Langone Medical Center in New York City.

"Anyone who is a shift worker probably warrants medical monitoring every six to 12 months," he says. These visits should include checking for high cholesterol, high blood pressure, and diabetes risks.

Shift Workers Can Trick Their Brains

"The findings add to a growing body of literature that bad sleep is bad for you. And one of the forms of bad sleep is [related to] shift work," says Steven H. Feinsilver, MD. He is the director of the Center for Sleep Medicine at Mount Sinai Medical Center in New York City.

Shift workers get less sleep than people who work a daytime schedule.

Most people can't up and quit their jobs, especially in this economy, but shift workers aren't powerless, Feinsilver says. "If you are going to work nights, get the darkest, best sunglasses you can find for going home in the morning so you avoid exposure to natural light."

Make sure your bedroom is cave-like -- dark, quiet, and cool. "When it's time to wake, turn on every light you can find," he says. These techniques can help trick your brain into thinking that it is night or morning so that you can get adequate sleep.